Avalanche Advisory
Advisory: Salt Lake Area Mountains Issued by Bruce Tremper for Tuesday - December 24, 2013 - 4:35am
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AVOID: backcountry travel today on any slope approaching 35 degrees and steeper (including locally-connected terrain) on slopes facing generally the north half of the compass plus east and west facing slopes, above about 8,000'. Avalanche danger is Level 3 (orange / considerable). This means "dangerous conditions...human triggered avalanches are likely...cautious route finding and conservative decision making are essential."

USUALLY-SAFE: You can find excellent turning, riding and snow shoeing on gentler slopes, less steep than about 30 degrees, in wind sheltered terrain not locally-connected to steeper terrain. In these conditions, backcountry travelers need excellent route finding and decision making skills learned in a field-based avalanche class.




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current conditions

It's warm and blustery this morning as a weak cold front approaches. It's near freezing at 8,000' with light snow falling. The rain-snow line is probably around 6,000' The ridge top winds have picked up and and are blowing 20-30 from the southwest with stronger winds on the higher peaks. Despite the graupel and dense snow that fell out of the last storm, the riding conditions remained surprisingly good. There is, however, a rime crust of various thickness in the high elevation terrain. See Trent Meisenheimer's primer on graupel and rime crust.

Here is a 2-day graph of temperature and precipitation at the Alta Collins weather station.
recent activity

Most people have heard about the avalanche incident inbounds at Alta. Skiers triggered a 2.5 - 3' deep, 100' wide slab on depth hoar on a west facing slope above the high traverse at 10,300'. Four people were caught and partially buried. Fortunately everyone is fine. In-bounds avalanches like this are extremely rare due to the hard work by the best avalanche teams in the country here in Utah who are out every morning knocking down avalanches with explosives before the public arrives. Although resorts are extremely safe, as we have seen, they can never be 100% safe.

Avalanche reduction work with explosives at Park City once again produced a couple large slides, on steep, east facing slopes at around 10,000'.

We did not hear about any avalanches triggered in the backcountry but with the poor visibility and dangerous conditions, few people were out pushing it.
Avalanche Problem 1
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 24 hours
description

We still have monsters in the basement on the shady aspects. A thick layer of weak, faceted snow is now buried a couple feet deep and people have triggered a dozen, large avalanches on this layer since Friday. Avalanche danger depends on BOTH probability and consequences. These will be more difficult to trigger today but they will be large-- 2 or more feet deep, plus in this shallow snowpack, even small avalanches will rake you through rocks and logs making the consequences much more serious than usual.

With a day of rest since the storm, I'm guessing the snowpack has settled a bit and i can drop it from Level 4 (High) danger yesterday to a Level 3 avalanche danger today (orange / sketchy / considerable--pick your term). This is for slopes generally facing the north half of the compass plus east and west facing slopes above about 8,000' on slopes approaching 35 degrees and steeper including locally-connected terrain. If you go to this terrain, keep your steepness under 30 degrees and out from underneath steeper slopes.

Here is an illustration from my book Staying Alive in Avalanche Terrain that illustrates that these persistent weak layers take a long time to settle out after a storm. Since most of us are impatient, persistent weak layers account for the vast majority of avalanche accidents.

Avalanche Problem 2
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 24 hours
description

You may be able to find several kinds of avalanches within the new snow. With continued strong winds from the southwest overnight, I expect we will have some dense wind deposits along the upper elevation, wind exposed terrain. As usual, avoid steep slopes with recent wind deposits. They usually look smooth and rounded. Also, even out of the wind, carefully check how well the new snow is bonded to the underlying layers. You can easily jump on small test slopes to see how they respond. Finally, watch for wet activity at lower elevations where the snowpack is wet and soggy.
weather

We have a weak cold front arriving this morning, which will give us 1-2 inches of new snow in the upper elevation terrain. It will start out quite warm with near-freezing temperatures at 8,000'. Ridge top winds will blow from the southwest 20-30 along the wind exposed ridges and stronger on the highest peaks. The cold air should arrive about mid day, winds should drop and skies should clear out this afternoon. It looks like more snow from this storm the farther north you go in Utah.

For the extended forecast, after this weak cold front, unfortunately we don't see any significant snow for at least the next 10 days.
general announcements

This information does not apply to developed ski areas or highways where avalanche control is normally done.  This advisory is from the U.S.D.A. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.

If you trigger an avalanche in the backcountry - especially if you are adjacent to a ski area – please call the following teams to alert them to the slide and whether anyone is missing or not. Rescue teams can be exposed to significant hazard when responding to avalanches, and do not want to do so when unneeded. Thanks.

Salt Lake and Park City – Alta Central (801-742-2033), Canyons Resort Dispatch (435-615-3322)

Snowbasin Resort Dispatch (801-620-1017), Powder Mountain Dispatch (801-745-3772 x 123).

Sundance Dispatch (801-231-4150)

DAWN PATROL Hotline updated daily by 5-530am - 888-999-4019 option 8.

Twitter Updates for your mobile phone - DETAILS

UDOT canyon closures:  LINK TO UDOT

Utah Avalanche Center mobile app - Get your advisory on your iPhone along with great navigation and rescue tools.

We'll soon be lining up a new automated emailed advisory delivery system - stay tuned.

Wasatch Powderbird Guides Blog/Itinerary for the Day.  They'll be up and running later this winter -

Lost or Found something in the backcountry? - http://nolofo.com/

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To those skinning uphill at resorts:  it is your responsibility to know the resort policy on uphill travel.  Some allow uphill travel and have guidelines, some don't. Contact the Ski Patrol at each resort for details. IMPORTANT: Before skinning at a resort under new snow conditions, check in with Ski Patrol.  Resorts can restrict or cut off access if incompatible with control and grooming operations.

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Remember your information can save lives. If you see anything we should know about, please participate in the creation of our own community avalanche advisory by submitting snow and avalanche conditions. You can also call us at 801-524-5304 or 800-662-4140, email by clicking HERE, or include #utavy in your tweet or Instagram.